Blast furnaces, systems used to smelt industrial metal, release high pressure and high temperature gases that can be utilized as a heat or electric source. The top gas that emerges from the top of the blast furnace is typically cleaned to remove large particulate matter, and used in a metal-producing plant as a fuel for heating or is fed into a top-pressure recovery turbine to generate electricity. Top-pressure recovery turbines (TRTs) are rotary mechanical devices used to extract energy from blast furnace gas by converting gas pressure and thermal energy to mechanical energy. Top-pressure recovery turbines generate power utilizing the expansion of gas volume with the reduction of its pressure. The high-temperature high-pressure gas enters the top-pressure recovery turbine where it expands down to the exhaust pressure, producing a shaft work output. The turbine shaft work can be used to power a device such as an electric generator coupled to the shaft. Generally, top-pressure recovery turbines increase the efficiency of blast furnace processes.
The composition of blast furnace gas (BFG) can vary based on the particular design of the blast furnace, its size, and the type of smelting. Blast furnace gas typically comprises ammonia, hydrochloric acid, sulfuric acid, nitrogen, carbon dioxide, carbon monoxide, sulfur dioxide, hydrogen, hydrogen sulfide, hydrogen cyanide, and water vapor at high temperature (e.g., greater than 70° C.) and elevated pressure (e.g., greater than 1 bar). Under certain conditions, acidic and basic blast furnace gases combine and precipitate to form deposits on turbine surfaces. For example, ammonia and hydrochloric acid combine to form ammonium chloride, a salt that readily adheres to turbine surfaces including the surfaces of blades and the inner cylinder.
Deposition of particulate matter on turbine surfaces can result in performance loss and equipment damage. For example, salt deposition on turbine blades can lead to blade work resistance, which results in a reduction in energy generated by the turbine. In addition, deposited salts can ionize into their respective acid and base, forming strong acid or base condensates on turbine surfaces. Strong acids and bases are corrosive substances that can destroy or damage metallic surfaces, which can lead to equipment damage and system failure.
Thus, it is important to prevent the formation of deposits and build-up of precipitates in top-pressure recovery turbine systems. Accordingly, there is a need for improved methods of limiting deposition of precipitates formed from blast furnace gases on the surfaces of top-pressure recovery turbine parts.